half-life

Examples of half-life in the following topics:

• Onset, Duration, and Half-Life of Hormone Activity

  • A hormone's half-life and duration of activity are limited and vary from hormone to hormone.
  • Vitamin D is a hormone that has a half-life of one to two months.
  • A hormone's half-life and duration of activity are limited and vary from hormone to hormone.
  • A biological half-life or elimination half-life is the time it takes for a substance such as a hormone or drug to lose half of its pharmacologic or physiologic activity.
  • In a medical context, half-life may also describe the time it takes for the blood plasma concentration of a substance to halve (plasma half-life) its steady-state.

• Half-Life of Radioactive Decay

  • Given a sample of a particular radionuclide, the half-life is the time taken for half of its atoms to decay.
  • The half-life is related to the decay constant.
  • Half-lives vary widely; the half-life of 209Bi is 1019 years, while unstable nuclides can have half-lives that have been measured as short as 10−23 seconds.
  • This means each half-life for element X is 18 days.
  • Nuclear half-life is the time that it takes for one half of a radioactive sample to decay.

• Half-Life

  • To find the half-life of the reaction, we would simply plug 5.00 s-1 in for k:
  • To find the half-life, we once again plug in $\frac{[A]_0}{2}$for [A].
  • Thus the half-life of a second-order reaction, unlike the half-life for a first-order reaction, does depend upon the initial concentration of A.
  • Rearranging in terms of t, we can obtain an expression for the half-life:
  • The half-life of a reaction is the amount of time it takes for it to become half its quantity.

• Half-Life of Knowledge

  • This phenomenon is what Gonzalez refers to as the "half-life" of knowledge - the time span from when knowledge is gained until it becomes obsolete (2004).
  • Since the advent of technology, from the radio to the internet, the half-life of knowledge has decreased significantly.

• Exponential Decay

  • As an example let us assume we have a $100$ pounds of a substance with a half-life of $5$ years.
  • Half-life is very useful in determining the age of historical artifacts through a process known as carbon dating.
  • C-13 has a half-life of 5700 years—that is, in 5700 years, half of a sample of C-13 will have converted to C-12, which represents approximately all the remaining carbon.
  • Using the graph, find that half-life.
  • Since there is 50% of the substance left after 1 year, the half-life is 1 year.

• Calculations Involving Half-Life and Decay-Rates

  • The half-life of a radionuclide is the time taken for half the radionuclide's atoms to decay.
  • The half-life of a radionuclide is the time taken for half of the radionuclide's atoms to decay.
  • A half-life must not be thought of as the time required for exactly half of the atoms to decay.
  • Note that after one half-life there are not exactly one-half of the atoms remaining; there are only approximately one-half left because of the random variation in the process.
  • The problems are taken from "The Joy of Physics. " This one deals with radioactive half-life.

• Dating Using Radioactive Decay

  • After one half-life has elapsed, one half of the atoms of the nuclide in question will have decayed into a "daughter" nuclide, or decay product.
  • Each step in such a chain is characterized by a distinct half-life.
  • The half-life of Cs-137 is 30 years.
  • First half-life (30 years): 100 grams of Cs-137 decays and 50 grams are left.
  • Calculate the age of a radioactive sample based on the half-life of a radioactive constituent

• Transuranium Elements

  • Each of these elements is radioactive, with a half-life much shorter than the age of the Earth.
  • Yellow - Radioactive elements: the most stable isotope has a half-life between 800 and 34.000 years.
  • Orange - Radioactive elements: the most stable isotope has a half-life between one day and 103 years.
  • Red - Highly radioactive elements: the most stable isotope has a half-life between several minutes and one day.
  • Purple - Extremely radioactive elements: the most stable isotope has a half-life less than several minutes.

• Half-Life and Rate of Decay; Carbon-14 Dating

  • Carbon-14 has a relatively short half-life of 5,730 years, meaning that the fraction of carbon-14 in a sample is halved over the course of 5,730 years due to radioactive decay to nitrogen-14.
  • Describes radioactive half life and how to do some simple calculations using half life.

• Still Life Painting

  • Still life painting flourished during the Golden Age of the Dutch Republic.
  • Virtually all still lifes had a moralistic message, usually concerning the brevity of life.
  • The vanitas theme was included in explicit symbols, such as a skull, or less obvious symbols such as a half-peeled lemon (representing life: sweet in appearance but bitter to taste).
  • Nevertheless, the force of this message seems less powerful in the more elaborate pieces of the second half of the century.
  • Discuss themes and attributes of 17th century Dutch still life painting